The conventional aeration pump for a fish globe (fish tank) or the like has a drawback of generating vibrational noise, especially at night; therefore, the globe has a electro-magnet circuit connected in series with a resistor or diode to limit the current so as to damp the vibration of the vibrating rod, whereby the noise is suppressed.
The aforesaid electro-magnet of aeration pump usually uses a "U" or "E"-shaped iron core, of which the opening portion has more magnetic reluctance, i.e. has more magnetic flux loss. The iron core should be wound with more turns of enamel wire; otherwise, the coil is susceptible to breaking because of having less inductance to cause the wire to be overheated.
In order to prevent the coil from being burned out, the aforesaid "U" or "E"-shaped iron core, just like the small transformer iron core, needs more turns of enamel wire to increase its reactance; further, the iron core is furnished with windings for both 120 V and 240 V AC power.
In the past, some aeration pumps have been mounted with a toy motor operated with DC power for outdoor fishing or in case of a power outage; however, the brushes of that motor are susceptible to damage after a long period of operation; it may be good for a short time or provisional operation.
In the conventional fish globes and fishing spot, the aeration pump is operated with a motor that is to be driven with either AC power or a dry cell battery, and that motor cannot be operated conveniently with either AC or DC power through a selective switch.
In the prior art, some aeration pumps use DC power to operate a multi-vibrator for generating a square wave to energize the electro-magnet; however, the vibration frequency of the electromagnet is susceptible to variation in case of the voltage having any variation for example, the vibration frequency is 60 Hz when the DC power is 6 V, upon the DC power being reduced to a level less than 6 V., the vibration frequency will also be lowered. As a result, the vibration amplitude will be reduced, and driving power to the aeration pump will also be reduced considerably.